1. Field of the Disclosure
The present disclosure relates to a liquid crystal display device that is configured to improve display quality by minimizing flickers and residual images.
2. Description of the Related Art
Generally, a liquid crystal display device controls the light transmittance of liquid crystal through the electric field, thereby displaying a picture. The liquid crystal display device includes a liquid crystal display panel where liquid crystal cells are arranged in a matrix shape. A drive circuit is used for driving the liquid crystal display panel.
In the liquid crystal display panel, as shown in FIG. 1, a gate line GL crosses a data line DL. A thin film transistor TFT for driving a liquid crystal cell is formed at the crossing point of the gate line GL and the data line DL. The thin film transistor TFT supplies a data voltage Vd through the data line DL to a pixel electrode Ep of the liquid crystal cell Clc in response to a scan signal supplied through the gate line GL. A gate electrode of the thin film transistor TFT is connected to the gate line GL and a source electrode is connected to the data line DL. A drain electrode is connected to the pixel electrode of the liquid crystal cell Clc. The liquid crystal cell Clc is charged with a potential difference between a common voltage Vcom supplied to a common electrode Ec and the data voltage Vd supplied to the pixel electrode Ep. The arrangement of liquid crystal molecules may be modified by an electric field, which is formed by the potential difference and may control the amount of the transmitted light or to intercept the light. The common electrode Ec is formed in an upper substrate or a lower substrate of the liquid crystal display panel through the application of the electric field to the liquid crystal cell Clc. A storage capacitor Cst for maintaining a charge voltage of the liquid crystal cell Clc is formed between the common electrode Ec and the pixel electrode Ep of the liquid crystal cell Clc.
Referring to FIG. 2, after a positive data voltage is supplied to a specific liquid crystal cell for a scan time (one horizontal period) of nth frame period Fn, a negative data voltage is supplied to the same liquid crystal cell for a scan time of the (n+1)th frame period Fn+1. For the nth frame period Fn, the liquid crystal cell is charged as much as the positive data voltage outputted from the data drive IC (D-IC). The cell then maintains a positive pixel voltage Vp(+) of which the absolute value is lowered by ΔVp below a charge voltage by a parasitic capacitance of the TFT. Conversely, for the (n+1)th frame period Fn+1, the liquid crystal cell is charged as much as the negative data voltage outputted from the data drive IC (D-IC), and then maintains a negative pixel voltage Vp(−) of which the absolute value is highered by ΔVp above the charge voltage by the parasitic capacitance of the TFT. Accordingly, even though the data voltage of the same gray level is supplied to the liquid crystal cell, the brightness and pixel voltage charged in the liquid crystal cell become higher in the negative data voltage than in the positive data voltage.
The positive pixel voltage Vp(+) of the liquid crystal cell is a difference voltage between a positive data voltage Vdata (+) and a common voltage Vcom, i.e., Vp(+)=|Vdata(+)−Vcom|. And, the negative pixel voltage Vp(−) of the liquid crystal cell is a difference voltage between a negative data voltage Vdata(−) and a common voltage Vcom, i.e., Vp(−)=|Vdata(−)−Vcom|.
Accordingly, if the polarity of the data voltage is inverted for each frame in the data of the same gray level, the brightness may be changed by the unit of a frame period, and as a result, an observer may notice a flicker phenomenon in that a screen periodically flickers. Further, if the pixel voltage charged in the liquid crystal cell is changed in accordance with the polarity of the data voltage, the residual image may appear on the screen because of the asymmetry of the data, thus the display quality may be further deteriorated.